4.1 Thermal Equilibrium
-
Upload
syazlina-samsudin -
Category
Documents
-
view
227 -
download
0
description
Transcript of 4.1 Thermal Equilibrium
4.1 UNDERSTANDING THERMAL
EQUILIBRIUM
Learning Outcome :
• Explain thermal equilibrium,
• Explain how a liquid-in-glass thermometer works
What changes has occurred ?
Temperature increases
Temperature decreases
Cold milk
Warm water
Faster rate
slower rate
Energy transferred
Net energy transferred (heat transferred) from water to milk.
What happen after sometime ?
Cold milk Warm water
Warms upCool down
No net heat transfer
The two objects are in thermal equilibrium
Thermal equilibrium
Common properties :No net heat transfer between the
objects Objects have the same temperature.
Instrument to measure temperature
Liquid-in-glass thermometer
• volume of liquid increases when it absorbs heat.
• Length of liquid column is directly proportional to the change of temperature.
Principle used :
How to measure temperature ?
The thermometer must be in thermal contact with the object.
Heat transferred occurs between the object and the liquid in thermometer. (From hot object to cold object).
After some time, the objects will reach thermal equilibrium. Both objects have the same temperature.
Therefore thermometer reading is the temperature of the object.
How to calibrate a thermometer ?
Liquid used : mercury can measure -39oC to 357oC
alcohol can measure -115oC to 78oC
Divide equally into 100 divisions.
Worked example
0
100 0
, 100oTemperature x C
The distance between the 0o C and 100oC scales marked on a thermometer is 28.0 cm. What is the temperature of water in container ?
Solution:
24.5100
28.0ocm
x Ccm
= 87.5 o C
EVALUATION
Two objects X and Y are brought into thermal contact. Initially X is hotter than Y. Indicate whether each of the statements is true (T) or False (F).
1. (a) There is transfer of heat energy between X and Y
(b) The temperature of X decreases.
(c) Y gives out more heat energy than it receives.
TT
F
EVALUATION
2. When X and Y have come into thermal equilibrium,
(a) Transfer of heat energy between X and Y
stops.
(b) The final temperature of X is higher than the initial temperature of Y.
(c) Heat energy is exchanged between X and Y at equal rates.
F
F
T
EVALUATION
Which of the following can increase the sensitivity of the thermometer ?A a large bulb B a long stem C a wide bore D a thin bulb wall
bulb stem bore
Diagram shows a mercury thermometer.